1. Field of the Invention
The present invention relates to a resonant charging type capacitor charging apparatus in which an inductance device and an energy accumulating capacitor resonate to charge the energy accumulating capacitor. In particular, the invention relates to a capacitor charging method and charging apparatus that prevent with high accuracy, an energy accumulating capacitor from being overcharged by inertial current, which is caused by magnetic energy stored in an inductance device.
2. Description of the Related Art
In a pulse laser such as an excimer laser, the charge of a capacitor for accumulating energy, which has been charged to a high voltage of approximately several kV to several tens of kV, is discharged at high speed to a laser tube via a magnetic compressor or the like, thereby exciting laser light. In an apparatus using a pulse laser, the higher the number of laser light excitations, that is, the higher the number of repetitions of charging and discharging the energy accumulating capacitor, the greater its capability as a laser apparatus. Therefore in recent years there have been attempts to achieve a high repetition rate of several kHz.
Consequently, the charging apparatus of the energy accumulating capacitor must be capable of repeated high-speed charging operations to completely charge it in less than several hundred xcexcs. Furthermore, excimer lasers require a highly accurate degree of voltage stability, detecting fluctuations in the output of laser light in each cycle and controlling the output of laser light in the subsequent cycle accordingly. Therefore, the charge voltage must be controlled in each cycle, making high-speed controllability an important feature.
FIG. 12 shows an example of a conventional resonant charging type capacitor charging apparatus. Reference numeral 1 represents a dc power supply obtained by rectifying ac power such as a commercial power supply. Reference numeral 4 represents a semiconductor switch such as an IGBT (Insulated Gate Bipolar Transistor) or the like, reference numeral 5 represents a resonant inductance device, reference numeral 7 represents a diode circuit, reference numeral 8 represents an energy accumulating capacitor, being a load, and these are connected to the dc power supply 1 equivalently, in series. Reference numerals 9 and 10 represent voltage detecting resistors. Reference numeral 3 represents a flywheel diode connected between the negative terminal of the dc power supply 1 and a node between the semiconductor switch 4 and the resonant inductance device 5. Reference numeral 14 represents a control circuit, which controls such that the semiconductor switch 4 is switched on by a charge start signal 16, and the semiconductor switch 4 is switched off when the voltage of the energy accumulating capacitor 8 reaches a target charge voltage VI supplied from a reference voltage power supply 15.
The operation will be described using FIG. 13. I represents the current flowing through the resonant inductance device 5, the white part is current flowing through the semiconductor switch 4, and the diagonally hatched part is current in which inertial current, occurring due to magnetic energy stored in the resonant inductance device 5, flows into the energy accumulating capacitor 8 through the flywheel diode 3 after the energy supply from the dc power supply 1 to the resonant inductance device 5 is stopped by switching off the semiconductor switch 4.
When the semiconductor switch 4 is switched on by the control circuit 14 on receiving the charge start signal 16 at time t0, resonant current flows due to the resonant inductance device 5 and the energy accumulating capacitor 8, and if no circuit loss occurs in components, wiring or the like by the flow of the charging current, the energy accumulating capacitor 8 is charged toward approximately twice the voltage value of the output voltage E of the dc power supply 1. When the charge voltage Vc, obtained by dividing the charge voltage of the energy accumulating capacitor 8 using the voltage detecting resistors 9 and 10, reaches the target charge voltage V1 at time t1, the control circuit 14 switches off the semiconductor switch 4. However, the flywheel diode 3 is switched on by inertial current due to the residual energy of the resonant inductance device 5, and continues charging the energy accumulating capacitor 8, which is overcharged by xcex94V.
Therefore, Japanese Unexamined Patent Application, First Publication No. Hei 8-9638 using a resonant charging scheme discloses a method in which power supply voltage is detected and added to a reference voltage out of phase, and the off timing of a semiconductor switch is adjusted such that variations of power supply voltage are compensated. However, the relationship between power supply voltage variation and excess charge amount is not linear, and in a real charger the final charge voltage always changes, so that it is not possible to improve the accuracy by only compensating for power supply voltage variation.
Accordingly, the present invention aims to provide a capacitor charging method and charging apparatus that can always charge an energy accumulating capacitor with highly accurate voltage stability, using a target charge voltage for the energy accumulating capacitor, and input voltage variation, even if the voltage of a dc power supply changes due to variations of a target charge voltage of the energy accumulating capacitor and an input voltage.
A capacitor charging method according to a first aspect of the present invention comprises the steps of: in a series connected circuit of a first semiconductor switch, a resonant inductance device, a diode circuit, and an energy accumulating capacitor, which are connected together in series to a dc power supply, starting charging of the energy accumulating capacitor due to the resonance of the resonant inductance device and the energy accumulating capacitor by switching on the first semiconductor switch; stopping energy supply from the dc power supply to the resonant inductance device by switching off the first semiconductor switch, when an equation Vc=xcex1((V12xe2x88x92Vo2)/(2E)+Vo) is satisfied, where V1 is a target charge voltage of the energy accumulating capacitor, Vc is a charge voltage of the energy accumulating capacitor, Vo is an initial voltage of the energy accumulating capacitor, E is an output voltage of the dc power supply, and a is a circuit loss coefficient for compensating for power loss occurring in components and wiring due to the flow of charging current; and after the first semiconductor switch is switched off, charging the energy accumulating capacitor to the target charge voltage V1 by the flow of inertial current caused by magnetic energy stored in the resonant inductance device, using a flywheel diode.
That is to say, charging is performed while calculating a forecast of the amount of added charge due to inertial current after the energy supply from the dc power supply to the resonant inductance device is stopped by the first semiconductor switch being switched off, and when it is determined by the calculation of the above equation that the energy accumulating capacitor can be charged to the target charge voltage by the inertial current, the first semiconductor switch is switched off, after which it is possible to charge to the target charge voltage with high accuracy using the inertial current.
A capacitor charging method according to a second aspect of the present invention comprises the steps of: in a series connected circuit of a first semiconductor switch, a resonant inductance device, a diode circuit, and an energy accumulating capacitor, which are connected together in series to a dc power supply, starting charging of the energy accumulating capacitor due to the resonance of the resonant inductance device and the energy accumulating capacitor by switching on the first semiconductor switch; stopping energy supply from the dc power supply to the resonant inductance device by switching off the first semiconductor switch, when an equation LI2=xcex1C(V12xe2x88x92Vc2) is satisfied, where I is a current flowing through the resonance inductance device, C is a capacitance of the energy accumulating capacitor, L is an inductance value of the resonant inductance device, V1 is a target charge voltage of the energy accumulating capacitor, Vc is a charge voltage of the energy accumulating capacitor, and xcex1 is a circuit loss coefficient for compensating for power loss occurring in components and wiring due to the flow of charging current; and after the first semiconductor switch is switched off, charging the energy accumulating capacitor to the target charge voltage V1 by the flow of inertial current caused by magnetic energy stored in the resonant inductance device, using a flywheel diode.
That is to say, charging is performed while calculating a forecast of the amount of added charge due to inertial current after the energy supply from the de power supply to the resonant inductance device is stopped by the first semiconductor switch being switched off, and when it is determined by the calculation of the above equation that the energy accumulating capacitor can be charged to the target charge voltage by the inertial current, the first semiconductor switch is switched off, after which it is possible to charge to charge to the target charge voltage with high accuracy using the inertial current.
The capacitor charging method according to the first or second aspect of the present invention may bypass the inertial current flowing into the energy accumulating capacitor by switching on a second semiconductor switch when the voltage of the energy accumulating capacitor reaches the target charge voltage V1 by means of the inertial current.
This is a capacitor charging method using a second semiconductor switch, which cuts off excess inertial current to the energy accumulating capacitor by bypassing it.
The capacitor charging method according to the first or second aspect of the present invention may switch on or off a second semiconductor switch that cuts off the inertial current flowing into the energy accumulating capacitor and may feed back the inertial current to the dc power supply when the voltage of the energy accumulating capacitor reaches the target charge voltage V1 by means of the inertial current.
This is a capacitor charging method using a second semiconductor switch, wherein inertial current to the energy accumulating capacitor is cut off, and this inertial current is fed back to the dc power supply.
A capacitor charging apparatus according to a first aspect of the present invention comprises: a first semiconductor switch, a resonant inductance device, a diode circuit, and an energy accumulating capacitor, which are connected together in series to a dc power supply; a first detecting device which detects an output voltage E of the dc power supply; a second detecting device which detects a charge voltage Vc of the energy accumulating capacitor; a computation section which outputs a signal for switching off the first semiconductor switch when an equation Vc=xcex1((V12xe2x88x92Vo2)/(2E)+Vo) is satisfied, using values detected by the first detecting device and the second detecting device, where V1 is a target charge voltage of the energy accumulating capacitor, Vo is an initial voltage of the energy accumulating capacitor, and xcex1 is a circuit loss coefficient for compensating for power loss occurring in components and wiring due to the flow of charging current; a first control section which charges the energy accumulating capacitor due to the resonance of the resonant inductance device and the energy accumulating capacitor by switching on the first semiconductor switch, and stops energy supply from the dc power supply to the resonant inductance device by switching off the first semiconductor switch, according to the signal from the computation section; and a flywheel diode which charges the energy accumulating capacitor to the target charge voltage V1 by means of the flow of inertial current caused by magnetic energy stored in the resonant inductance device after the first semiconductor switch is switched off.
This is a capacitor charging apparatus using the first aspect of a capacitor charging method.
A capacitor charging apparatus according to a second aspect of the present invention comprises: a first semiconductor switch, a resonant inductance device, a diode circuit, and an energy accumulating capacitor, which are connected in series to an de power supply; a current detecting device which detects a current I flowing through the resonant inductance device; a voltage detecting device which detects a charge voltage Vc of the energy accumulating capacitor; a computation section which outputs a signal for switching off the first semiconductor switch when an equation LI2=xcex1C(V12xe2x88x92Vc2) is satisfied, using values detected by the current detecting device and the voltage detecting device, where C is a capacitance of the energy accumulating capacitor, L is an inductance value of the resonant inductance device, V1 is a target charge voltage of the energy accumulating capacitor, and xcex1 is a circuit loss coefficient for compensating for power loss occurring in components and wiring due to the flow of charging current; a first control section which charges the energy accumulating capacitor due to the resonance of the resonant inductance device and the energy accumulating capacitor by switching on the first semiconductor switch, and stops energy supply from the dc power supply to the resonant inductance device by switching off the first semiconductor switch, according to the signal from the computation section; and a flywheel diode which charges the energy accumulating capacitor to the target charge voltage V1 by means of the flow of inertial current caused by magnetic energy stored in the resonant inductance device after the first semiconductor switch is switched off.
This is a capacitor charging apparatus using the second aspect of a capacitor charging method.
The capacitor charging apparatus according to the first or second aspect of the present invention may further comprise: a second semiconductor switch which bypasses the inertial current to the energy accumulating capacitor; and a second control section which switches on the second semiconductor switch when the charge voltage of the energy accumulating capacitor reaches the target charge voltage V1 by means of the inertial current, using values detected by the first detecting device and the second detecting device, or the current detecting device and the voltage detecting device.
This is a capacitor charging apparatus using a capacitor charging method, wherein excess inertial current flow into the energy accumulating capacitor is cut off by being bypassed.
In the capacitor charging apparatus according to the first or second aspect of the present invention, the second semiconductor switch may be connected in parallel to both terminals of the energy accumulating capacitor, and the diode circuit may be connected between the second semiconductor switch and the energy accumulating capacitor.
Here, a step-up transformer may be further provided in between the resonant inductance device and the second semiconductor switch, and the resonant inductance device may include leakage inductance of the transformer.
In the capacitor charging apparatus according to the first or second aspect of the present invention, the first semiconductor switch may be a bridge inverter circuit, which is provided with four semiconductor switches in two pairs, and flywheel diodes connected in reverse parallel to these semiconductor switches respectively.
In a capacitor charging apparatus of the first aspect or second aspect of the present invention, the diode circuit may be a full bridge circuit, a half bridge circuit or a diode.
The capacitor charging apparatus according to the first or second aspect of the present invention may further comprise: a second semiconductor switch which cuts off the inertial current to the energy accumulating capacitor; and a second control section which switches on or off the second semiconductor switch when the charge voltage of the energy accumulating capacitor reaches the target charge voltage V1 by means of the inertial current, using values detected by the first detecting device and the second detecting device, or the current detecting device and the voltage detecting device, and feeds back the inertial current to the dc power supply.
This is a capacitor charging method using a second semiconductor switch that cuts off inertial current to an energy accumulating capacitor.
Here, one end of the second semiconductor switch may be connected to a node between the resonant inductance device and a diode for preventing reverse flow, via the diode for preventing reverse flow, and the other end may be connected to the dc power supply.
In addition, one end of the second semiconductor switch may be connected to a node between the resonant inductance device and the diode circuit via a diode for preventing reverse flow, and the other end may be connected to the de power supply.
As described above, in the present invention, charging is performed while calculating a forecast of the amount of added charge due to inertial current after the energy supply from the dc power supply to the resonant inductance device is stopped by the semiconductor switch being switched off, and when it is determined that the energy accumulating capacitor can be charged to the target charge voltage by the inertial current, the first semiconductor switch is switched off, and afterwards the inertial current charges it to the target charge voltage.
Furthermore, a second semiconductor switch for bypass or cutoff is provided, separate to the first semiconductor switch which starts charging the energy accumulating capacitor, being a load. The energy accumulating capacitor is charged by the resonance of the resonant inductance device and the energy accumulating capacitor when the first semiconductor switch is switched on, and before it is charged to the target charge voltage, the first semiconductor switch is switched off. Afterwards, when the energy accumulating capacitor reaches the target charge voltage, in a first method the second semiconductor switch is switched on, excess charging current to the energy accumulating capacitor is cut off by being bypassed, and overcharging is prevented, giving a highly accurate charge. Moreover, in a second method, the second semiconductor switch is switched on or off, excess charging current to the energy accumulating capacitor is cut off, and overcharging is prevented, giving a highly accurate charge.
In this manner, in the present invention, the first semiconductor switch and the second semiconductor switch are controlled by two control circuits, and thus charging is controlled while calculating a forecast of the amount of overcharging of an energy accumulating capacitor caused by inertial current from the resonant inductance device of a capacitor charging circuit, and when the energy accumulating capacitor is charged to a target charge voltage by the inertial current, by switching the second semiconductor switch on or off, it is possible to achieve an extremely highly accurate degree of stability of charge voltage of an energy accumulating capacitor such as an excimer laser source and the like.